This invention relates to heating chambers such as hot air sterilizers, ovens and the like, and more particularly to a heating cabinet which utilizes an antechamber construction that requires only a single heating element to provide adequate, uniform heating of the interior portions of the cabinet. Such heating cabinets have been used for the most varied purposes for a long time. It has been considered necessary to construct the heater in multipart manner due to the advantageous parallelepipedic construction. Separate heaters have at least been provided for the vertically superimposed side parts and the base part, whereby each of said heaters has had to be provided with two connections for securing and conducting electric power or a hot heat transfer agent. It is therefore necessary to provide for the two side parts and the base three heaters with a total of six connections. This naturally had led to considerable expenditure, not only for the production of the three different heaters with their connection, but also in connection with the fitting and assembly. Thus, the six connections must obviously also be fitted.
Apart from the aforementioned meander-like heating rods, straight heating rods have also been used, which are externally fixed to the boiler and indirectly heat the same. However, in general, much larger numbers thereof must be used, so that the aforementioned disadvantage is exacerbated compared with the meander-like construction, which has the advantage of being able to heat a larger area. However, these heaters lead to control problems linked with their large mass, which leads to a high time constant. In addition, boilers made from relatively poor heat conducting material cannot be heated, because the high heating density given off by the heater over the contact surface between the latter and the boiler cannot be transferred away without considerable warping of the boiler material.
In addition, in the case of special constructions, such rod-like heaters are also arranged in exposed manner in the heating chamber, which also causes a cleaning problem for the boiler.
In addition, finned radiant heating also exists in which the inner walls of the boiler have fin-like portions, in which are fitted heating conductors insulated by ceramic beads. Quite apart from extremely time-consuming fitting and difficulties connected with their repair, the spatial temperature uniformity is unsatisfactory, particularly when the fins approach the boiler walls. As in the case of the previously described process, the heaters are in contact with the boiler walls, so that they have a much higher temperature than the air in the boiler.
Moreover, integral fin tube heaters are known and are used for equipping space heaters, warming cabinets, domestic baking ovens, heating compartments and the like. They also have beadinsulated heating coils, held by an integral fin tube, which is open at one side. Here again, at least two heaters are required, even in the case of relatively flat boilers, such as e.g. domestic ovens. In the case of higher boilers or applications requiring good temperature uniformity, the side walls must be additionally heated by means of elongated fin tube heaters (Brochure of Blanc and Fischer, 7135 Oberderdingen).
Circulating air cabinets are also known, which have an antechamber extending over only part of the rear wall of the work space. The fresh air is sucked in from behind and is directed against the rear wall by means of a radial fan through the aforementioned relatively small antechamber. As soon as the air has left the antechamber, it is forced towards the sides on the cold inner walls and up to the front wall and is then sucked rearwards again in the centre of the work space. There is consequently a constant cooling of the air on its path from the heater back to the air duct. This more particularly applies with respect to the air masses flowing past the cold, unheated side walls of the boiler and its bottom, so that there is a temperature gradient within the cabinet (Brochure of Messrs A. Hoffman, 7302 Nellingen).